The day Christopher Nolan called Cillian Murphy about his new film, “Oppenheimer,” Murphy hung up the phone in disbelief. As Nolan has said, “Like it or not J. Robert Oppenheimer is the most important person who ever lived.” “Oppenheimer,” which opens in theaters on July 21, features a starry cast including Emily Blunt as Oppenheimer’s wife Kitty, Matt Damon as …